Human Colony Demographics

LiptonCambell
LiptonCambell: If you were going to setup a human colony on a distant planet, what is the
minimum number of couples you would need to create a viable long term
human population? The assumption is that there would be no contact with Earth
for centuries, and their mandate is to produce as many children as necessary.
Second question. Assume modern longievity and mortality, what would the
population increase be every generation?
12 years ago Report
0
StuckInTheSixties
StuckInTheSixties:

Hmm ... I have no answers for this, only uneducated guesses.

Guess 1.
It would probably require quite a few people to set up a colony that is guaranteed never to have any outsiders to add new genes to the pool. One thing that would help the colony to thrive (genetically) would be the abandonment of monogamy in lieu of genetic diversity.

Guess 2.
It would depend on all sorts of factors. I don't know if there's an answer to that. Is there?

12 years ago Report
0
cuarl
cuarl: I think this has alot to do with chance. Ultimately its the more couples the better ofc. But if they are lucky and healthy then perhaps even one couple could do it.
10 babies. 2boys, 8 girls. Those 8 girls give birth to 10 babies from the 2boys. It wouldnt be pretty but it might work with some luck.

Our universe is built on random and chance after all.
12 years ago Report
0
StuckInTheSixties
StuckInTheSixties:

Ever hear of "inbreeding"?

12 years ago Report
0
cuarl
cuarl: Yes ofcourse. I didnt say it would be pretty or even succeed. I said that one healthy couple could do it with luck. Our universe is built on chance so there is no optimal number but simply, the more the better.
(Edited by cuarl)
12 years ago Report
0
StuckInTheSixties
StuckInTheSixties:

Mom and Dad and kids ... one happy inter-boinking family ...

Yep, you're right. Not pretty ...



12 years ago Report
0
LiptonCambell
LiptonCambell: Oh come on Stuck- there had to be alot of inbreeding for this many people to be here....chances are inbreeding is more common than not, historically
12 years ago Report
0
StuckInTheSixties
StuckInTheSixties:

Of course. Fuckin' cousins.

But the mom/dad/bro/sis swinger's party doesn't strike me as the healthiest gene pool. There's an old Robert Heinlein sci-fi story, "Farnam's Freehold," that examines the question of a sudden necessary tiny gene pool.

en.wikipedia.org/wiki/Farnham's_Freehold

12 years ago Report
0
Serabi
Serabi: What are the demographic risks?

- Demographic stochasticity

- Environmental variation (year to year)

- Catastrophes (episodic extreme events)

12 years ago Report
0
Serabi
Serabi: My first thoughts were of the Indian Continent. Because of some epic extinction thousands of years ago (A vague memory, I can't remember specifics) it is estimated that the huge population has grown from about 5000 individuals. Conjoined twins in India is more prevelant that anywhere else. It might be the following:-

Toba Lake in northern Sumatra is the world's largest active volcanic caldera. The volcanic eruption that resulted in Lake Toba (100 x 30 km) 74,000 years ago, is known to have been by far the biggest eruption of the last 2 million years. This mega-bang caused a prolonged world-wide nuclear winter and released ash in a huge plume that spread to the north-west and covered India, Pakistan, and the Gulf region in a blanket 1–5 metres (3–15 feet) deep. Toba ash is also found in the Greenland ice-record and submarine cores in the Indian Ocean, allowing a precise date marker. In our story the Toba eruption is the most accurately dated, dramatic, and unambiguous event before the last ice age.

Toba is also regarded by some as having caused worldwide population extinctions as a result of the ‘nuclear winter’ that followed. I have taken this into account in my reconstruction. India bore the brunt of the massive ash fall, and may have suffered mass extinction, since the Toba plume spread north-west across the Indian Ocean from Sumatra. This event may explain why most Indian maternal genetic sub-groups of the two founder lines M & N are not shared elsewhere in Asia and the dates of their re-expansions are paradoxically younger in India than elsewhere in East Asia and Australasia.


The following is also of interest.

KILLER GENES

Indian Parsis traveled to other parts of the world to settle down in every continent, yet, the total number of Parsis today is an alarming 63,000. It was determined in a long drawn legal battle that ended in 1908 that you had to be born a Parsi, you could not convert to become one. You could become a Zoroastrian but not a Parsi. So, Parsis married within their limited community and as happened with Egyptian nobility thousands of years ago, the Parsi blood thinned and became a feeding ground for genetic diseases. The killer genes simply got passed down the line until Parsis are now a community prone to hemophilia, osteoporosis and cancer.

For many years, inter-community marriages were heavily frowned upon but today, it may be the only means of saving a vibrant group of people from dying out on us. And it is not just the race that is in jeopardy of extinction. The entire Parsi tradition, if you recall, was orally transmitted down the ages. With a thinning number in the younger generations and a larger group of elders, this tradition is in vital need of documentation and preservation. The UNESCO has made a gesture in this direction by creating a forum and giving a small donation as seed money for a project (called Parjor) to retrieve and record what is left of the Parsi way of life. The project coordinator, the dynamic Dr Shernaz Cama says: "The project is in desperate need of help, from both Parsis and others who are interested in preserving this community's history. We need men, materials and money. To travel to places, document stories, legends and artifacts on film and even physically. We plan a museum, a library and films."

11 years ago Report
0
Geoff
Geoff: Surely a humanity with the technology required to make even a 'generational' stellar spacecraft would also have sufficient mastery of genetics to deal with the problems of inbreeding.

Alternatively you wouldn't necessarily need a supply of couples, just a healthy number of women and a ready supply of frozen sperm from a variety of donors - or even genetic material taken from each other. That would solve the inbreeding.

Then you just need a sufficiently large and diverse population to survive disease, famine, plagues of alien-locusts...
11 years ago Report
1
Serabi
Serabi: Nature does not like being messed with. Somewhere a price is paid.
11 years ago Report
0
LiptonCambell
LiptonCambell: Lol good answer Geoff!

Serabi- you mention this mass extinction event- this may be a stupid question, but you didn't mention it, and I haven't researched it- is there evidence of any other lifeforms going extinct? or is it just supposed the human population shrunk because there is less genetic diversity in India(ha...In India)

Like, is there any evidence of an extinction event outside of a lowered genetic diversity in that region?
11 years ago Report
0
Serabi
Serabi: Copied and pasted:-

The mighty volcano that may have altered the course of human evolution.

What is Toba?

Toba today is a beautiful lake on the island of Sumatra in Indonesia. It claims the title of having the largest island within an island, Samosir. It is popular tourist destination and attracts many who are seeking gorgeous vistas and relaxation.

However, it's highly unusual for lakes the size of Toba to form on islands. So your next question might be:

But What Was Toba?

Toba was a supervolcano that erupted approximately 73,500 years ago. It is considered by geologists to have been the largest volcanic eruption within the past 20 million years. The eruption lasted two weeks. Core samples evidence ash layer deposits of 3 meters in some parts of India and 10-12 centimeters in the Indian Ocean. The island of Samosir formed as a "resurgent dome" to cap off the last explosions of Toba's supereruption.1


What is a Supervolcano?

A supervolcano is like a regular volcano in that it is a geologic phenomenon in which the buildup of magma causes an eruption through the earth's crust of hot molten rock and volatile gases. However, a supervolcano's eruption is on a considerably larger scale.

All volcanoes are measured on what is called the Volcanic Explosivity Index (VEI). Eruptions are categorized on a range of 0 to 8, with a score of 8 being reserved for only the most cataclysmic of eruptions. Each gradation in the range represents an eruption that is ten times as powerful than the previous categorical gradation. The largest eruption in recorded human history, Tambora, received a VEI score of 7. Toba received a score of 8.

Supervolcanoes don't look like regular volcanoes. They do not form familiar conical shapes like Mount St. Helens or Mount Fuji. Instead, they form large crater-like depressions in the earth called calderas. Rather than breaking the surface via periodic eruptions like other volcanoes, magma from the earth's core concentrates just beneath the crust, building up an unbelievable amount of pressure for tens, even hundreds of thousands of years. Once this pressure becomes too much for the brittle layer of crust containing it, the magma breaks through, expelling a titanic volume of ash and gases way up into the upper atmosphere. After the super-eruption, the earth's crust collapses and forms the caldera depression.


Eruptions with the magnitude of a supervolcano occur infrequently, on average once every 50,000 years.2 This is pretty fortunate since the volume of volcanic materials expelled is many times greater than any volcano man has experienced in human history. Because of their scale, super-eruptions have the potential to severely alter the world's climate which has some devastating effects on world agriculture, vegetation, animal life and humans.

What were the effects on global climate?

The debris kicked up by a supervolcano is essentially enough to create an atmospheric veil that absorbs and reflects the sun's rays back into space. This would in turn serve to cool the earth as it blocks solar radiation from reaching the surface of the planet. Scientists term the climatic aftereffects of a supereruption a Volcanic Winter.

Toba occurred during a global transition from a relatively warm, humid climate to that of a colder one marked by increased ice and snow accumulation (Oxygen-Isotope Stage 5a-4 Boundary). During this period, sea levels and sea-surface temperatures were dropping considerably, but only gradually. Toba may have been just the impetus needed to accelerate the shift.


The supereruption of Toba released 2,800 cubic kilometers of magma and anywhere from between1,000 to 10,000 metric tons of volcanic ash , dust and sulfuric aerosols into the atmosphere.2 As stated previously, these volcanic materials serve to create a veil surrounding the earth, blocking the sun's radiation from reaching (and heating) the Earth's surface. Rampino asserts that aerosol loading of just 1,000 metric tons would have been enough to cause a global cooling of 3° to 5° Celsius, with regional drops of up to 15°C.

It follows then that the climatic aftermath of Toba effectively devastated the world's ecosystem from the bottom of the foodchain upwards. Since plant life relies on photosynthesis, any decrease in sunlight would have a damaging effect on the world's vegetation. Fauna adapted to relatively tropical, warm climates would essentially die off in a matter of weeks. Even hardier vegetation in the temperate regions would begin to suffer. Studies have shown that while hardy vegetation fares relatively well during sub-normal temperature and sunlight dips in the winter, during the warmer growing season, any sustained dip over the course of several years could prove fatal. Additionally, oceanic concentrations of algae and phytoplankton, which also survive by nature of photosynthesis, would suffer, consequently destroying much of the sea's fragile ecosystem. Given that scientists believed the atmospheric effects of Toba lasted for 6 years, once could imagine quite a bit of Earth's plant life suffered in the aftermath.

What are the main theories for the origin of modern humans?

There are two main theories: the first is the multiregional hypothesis, which says that modern humans evolved generally at the same time in several regions, and gene flow between groups accounts for them not evolving into different species. The second, the Out of Africa or replacement hypothesis, says that modern humans evolved in Africa and then moved out to other parts of the world, replacing hominids that were already there. DNA studies support the Out of Africa hypothesis, and it is now more widely accepted.4


There is a hypothesis, the “weak Garden of Eden” model, which is a version of the Out of Africa theory. It suggests that humans dispersed from Africa about 100,000 years ago, suffered from a population bottleneck, and then recovered. The timing of Toba roughly matches the timing of the population bottleneck. Genetic evidence backs this up: since Africa, situated primarily on the equator, had the largest areas where humans could survive the volcanic winter, it retained a larger human population. A larger bottleneck in Africa explains why African populations have a higher genetic diversity; populations passing through smaller bottlenecks in other parts of the world would have less genetic diversity, and this is indeed seen in the DNA evidence.

What were the particular effects of Toba on human evolution?

At the time Toba erupted, 74000 years ago, humans had already spread out of Africa into other regions such as southern Asia and the Middle East. They had not yet reached the Americas, Europe, or Australia, although it has been argued that about 70,000 years ago, as a result of the ice age caused by Toba, sea level dropped enough that humans could island-hop their way over to Australia. Toba erupted at a bad time for human populations: the ice expanses in northern Eurasia were expanding, making humans retreat southward, and migrating groups were spreading out of Africa.

The Toba-induced volcanic winter hit these small bands hard, reducing their numbers drastically; in what is known as a population bottleneck, the worldwide human population shrank to as small as 10,000 people or even less (estimates vary). The temperature drop and climatic effects around the world hit populations in higher latitudes the hardest; humans most likely to survive were those who lived in tropical regions, where the temperature would be warmer. The largest of these “tropical refugia” was in Africa, near the equator; this is backed up by the fact that the most genetic diversity in humans is found in Africa. The genetic evidence also tells us that there was an extinction event in INDIA around the time of the Toba eruption. This can be explained if we remember that the ash cloud produced by Toba would have hit the area around the Indian Ocean the hardest; humans in that area were wiped out, and then the region was recolonized from the east and west.

11 years ago Report
0
Serabi
Serabi: I can't find any specifics on other Animal extinctions. Only this:-

Genetic bottlenecks of other mammals

The eruption may had also caused bottlenecks or extinctions in some animals (especially those in Southeast Asia, India, far north as China and as far west as Europe and Africa). The population of the Eastern African chimpanzee, Bornean orangutan, central Indian macaque, the cheetah, the tiger, and the separation of the nuclear gene pools of eastern and western lowland gorillas, all recovered from very low numbers around 70,000–55,000 years ago.
(Edited by Serabi)
11 years ago Report
0
Geoff
Geoff: Humanity hit a fairly significant bottleneck upon leaving Africa.

Which is why there is many times more genetic diversity in sub-saharan Africa than in the rest of the world combined.
11 years ago Report
0
sodsfoipsdfj
(Post deleted by staff 11 years ago)
Serabi
Serabi: I think it takes a lot of courage, desperation or starvation for people to enter the completely unknown. Hunter gatherers follow their prey animals. Folks flee their pursuers. Hence a smaller gene pool. Just a guess.
11 years ago Report
0
Geoff
Geoff: Well, they (anthropologists) reckoned that humanity spread (on average) over 40km per generation.

Considering the geometric growth of populations, that meant that humanity covered the planet very quickly. But from the origins in Africa, there was only a fraction of the human population who spread out through the middle east to the rest of the planet. Still a very large number, but proportionally small.

The last time I looked into this issue there was still some questions about the origins of the aboriginal people of Australia. It wasn't clear if they were part of the 'bottleneck' population or an entirely separate emigration from Africa. This was some years ago, so I guess that question has been settled now. I really should look it up.
11 years ago Report
0
ergghdfg
(Post deleted by staff 11 years ago)